Methods for vehicle speed accuracy compensation

Abstract

A method and system for calibrating a speed displayed in a vehicle is provided. In one example, a method includes adjusting a determination of vehicle speed responsive to character recognition of an image from an on-board camera of the vehicle, the image including an external speed measurement source (such as a radar speed sign) displaying a speed measurement. The speed displayed in the vehicle may be corrected if the determined vehicle speed is outside of a threshold range generated from the speed measurement displayed on the external speed measurement source.

The invention claimed is: 
     
       1. A method, comprising:
 adjusting a determination of speed of a motor vehicle responsive to character recognition of an image from an on-board camera of the vehicle, the image including a speed measurement source external to the vehicle, and controlling power output of a motor propelling the vehicle based in part on a difference between a desired vehicle speed and the adjusted determination of vehicle speed to achieve the desired vehicle speed. 
 
     
     
       2. The method of  claim 1 , wherein the determination of vehicle speed is based on output from wheel speed sensors positioned in the vehicle to measure a rotational speed of wheels of the vehicle. 
     
     
       3. The method of  claim 1 , wherein the speed measurement source is a radar speed sign. 
     
     
       4. The method of  claim 1 , wherein adjusting the determination of vehicle speed includes adjusting a speed displayed on a speedometer of the vehicle. 
     
     
       5. A method comprising:
 determining a speed of a motor vehicle based in part on output of sensors positioned on-board the vehicle; 
 determining a reference speed of the vehicle based in part on on-board character recognition of a speed measurement source external to the vehicle; and 
 correcting the determined vehicle speed when the determined vehicle speed is outside of a threshold range, the threshold range generated from the determined reference speed responsive to an indication that the speed measurement source external to the vehicle is functional. 
 
     
     
       6. The method of  claim 5 , wherein the vehicle speed is determined using a vehicle speed module and output from wheel speed sensors, and the reference speed is determined from a radar speed sign, the radar speed sign being identified using an on-board camera of the vehicle and an image recognition module. 
     
     
       7. The method of  claim 5 , wherein the threshold range is defined by a first, lower threshold and a second, higher threshold, with the first threshold being a percentage less than the determined reference speed and the second threshold being a percentage more than the determined reference speed. 
     
     
       8. The method of  claim 5 , wherein correcting the determined vehicle speed comprises:
 determining a vehicle speed compensation based on the determined vehicle speed and the determined reference speed; and 
 applying the vehicle speed compensation to the determined vehicle speed to generate a corrected vehicle speed. 
 
     
     
       9. The method of  claim 8 , wherein the corrected vehicle speed is displayed on a speedometer of the vehicle. 
     
     
       10. The method of  claim 5 , wherein determining that the speed measurement source external to the vehicle is functional comprises indicating an absence of an object between the vehicle and the speed measurement source external to the vehicle based on data from one or more of an on-board camera and an on-board radar system. 
     
     
       11. The method of  claim 10 , wherein determining that the speed measurement source external to the vehicle is functional further comprises:
 determining a change in the vehicle speed over a duration; 
 determining a change in the reference speed over the duration; and 
 indicating that the speed measurement source external to the vehicle is functional responsive to the change in vehicle speed being within a predetermined threshold of the change in the reference speed. 
 
     
     
       12. A system for a vehicle, comprising:
 an engine configured to propel the vehicle; 
 a plurality of wheels; 
 wheel speed sensors configured to measure a number of revolutions over time of each of the wheels; 
 a camera; 
 a radar system; 
 a speedometer; and 
 a controller storing instructions in non-transitory memory that, when executed, cause the controller to:
 receive images captured by the camera and determine an external speed measurement in the images using an image recognition module; 
 calculate vehicle speed using a vehicle speed module and output from the wheel speed sensors; and 
 apply a vehicle speed compensation to the vehicle speed module responsive to the calculated vehicle speed being outside of a threshold range determined from the external speed measurement, the calculated vehicle speed and the external speed measurement being time-matched speed values, to generate a corrected vehicle speed. 
 
 
     
     
       13. The system of  claim 12 , wherein determining the external speed measurement in the images further includes determining an absence of an object between the vehicle and a source of the external speed measurement based on data from the radar system. 
     
     
       14. The system of  claim 12 , wherein the vehicle speed compensation is determined from a difference of the calculated vehicle speed and the external speed measurement. 
     
     
       15. The system of  claim 12 , wherein the corrected vehicle speed is displayed on the speedometer. 
     
     
       16. The system of  claim 12 , wherein the controller further stores instructions in non-transitory memory that, when executed, cause the controller to:
 adjust a power output of the engine responsive to the calculated vehicle speed being determined as different from a desired vehicle speed.